Police in the city of Detroit, in the US state of Michigan, have released a graphic 68-second video showing a gunman striding into one of the city's precinct stations, and spraying volleys from a shotgun at surprised officers before being fatally wounded as he stood within inches of three of his victims.

The grainy surveillance video from the rampage at the sixth Precinct has been made public only after members of the city's police force had seen it.

The video shows Lamar Moore, 38, walking into the precinct and past the raised front desk.

He pulls a shotgun he had concealed along his left side and opens fire down a hallway, hitting a female sergeant in her bullet-proof vest.

With Commander Brian Davis and a sergeant firing shots in his direction, Moore then lunged head first onto, then over, the front desk counter towards them and two other already wounded officers.

On the video, Davis fell and dropped the gun he had been firing, but twisted around a smaller desk as Moore continued towards him. Moore, himself wounded, attempted to manoeuvre toward Davis, but fell to the floor. He later died while being taken to hospital.

Four officers were wounded. Davis, the most seriously injured, was also shot in the back.

He and Sergeant David Anderson are expected to be released from the hospital soon.